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The Oyster’s Gem: As the Pearl Turns

This article was originally posted on RealClearScience.

The first person who discovered pearls must have believed he stumbled across a bit of magic. Pull apart the valves of a living oyster, and a beautiful spherical gem of calcium carbonate may lay inside. Alas, it is not magic. A pearl forms in response to tissue damage, such as by the introduction of a foreign body, and the pearl is the oyster’s attempt to wall off the offending object. (A similar process occurs in the lungs of people with tuberculosis.) Today, humans take advantage of this quirk of oyster biology in order to culture pearls on our own terms.

Though the basic biology of pearl formation is understood, many mysteries endure. For instance, small circles, rings, and other imperfections form on the surface of pearls. (See figure.)

This indicates that the pearl rotates during its formation, but this process has never been directly observed because it is rather difficult to witness such a phenomenon inside a living creature. So a team of researchers devised a clever way to investigate pearl rotation. Their results are published in the journalRoyal Society Open Science.

The scientists implanted tiny magnetic beads inside of oysters, around which pearls began to form. The oysters were then placed inside of a magnetometer which detected the movement of the magnetic beads. (See figure.)

The figure depicts the formation of two different pearls. For pearl #1, there was no rotation for the first 40 days (figure A), after which the pearl began to rotate (figure B). For pearl #2, there was no rotation for the first 24 days (figure C), after which the pearl began to rotate (figure D). On average, the pearls rotated at a speed of 1.27 degrees per minute, which means a full rotation took approximately 4 hours and 43 minutes.

The team concluded that following an initial period of random movement that can last up to 40 days, the pearl begins a stable rotation which endures for 12-18 months, the time required for a pearl to form.

Finally, the authors added a small, endearing rhetorical flourish: “Nature’s ability to generate so amazingly complex structures like a pearl has delivered one of its secrets.” A finer statement of the grandeur of pure scientific discovery has rarely been written.